1. Field of Invention
The present invention relates generally to a combined global positioning system receiver and radio unit. More specifically, the present invention relates to a combined global positioning system navigation unit and two-way radio communications unit that includes a substantially waterproof enclosure for protection of the electronic components contained therein, and method of fabrication of the substantially waterproof enclosure.
2. State of the Art
A global positioning system (GPS) is an electronic satellite navigation system that permits a user of the system to determine his or her position with respect to the Earth. Global positioning may be accomplished through the use of a handheld GPS receiver device that detects and decodes signals from a number of satellites orbiting the Earth. The signals from each of these satellites indicate the position of the satellite and the time at which the signal was sent. To decode the satellite signals, known as spread spectrum signals, and thereby calculate the desired navigational data, a GPS receiver must first “find” or acquire the signals emitted from a minimum number of satellites. Once the receiver is “locked on” to the spread spectrum signals, continuous real-time calculation and monitoring of the user's global position and other navigational data (e.g., velocity of movement) may be performed.
GPS receivers have clocks that are synchronized with clocks in each of the satellites to determine how long it takes the signals to travel from the satellites to the receiver. In this regard, GPS receivers require a highly accurate internal frequency reference in order to acquire the spread spectrum GPS satellite signals. Specifically, acquiring spread spectrum satellite signals from a sufficient number of satellites to perform calculations requires determining the frequency of oscillation of the crystal oscillator utilized in the GPS receiver.
Once the GPS receiver has acquired and decoded signals from a minimum of three satellites, the GPS receiver can calculate the user's position (i.e., latitude and longitude) by geometric triangulation. Upon acquiring signals from a minimum of four satellites, the GPS receiver can also calculate the user's altitude. In addition, GPS receivers are able to calculate the user's speed and direction of travel by continuously updating the user's position. Accordingly, GPS receivers are highly valuable and widely used in navigational systems because of their ability to accurately compute the user's position on or near the Earth in real-time, even as the user is moving.
In addition to the growing popularity and demand for GPS navigational devices, portable two-way radios continue to enjoy widespread popularity. In 1996, the Federal Communications Commission (FCC) established the Family Radio Service (FRS) so that families and other small groups could communicate with one another over very short distances (typically less than one mile) at no charge and without an FCC license. The FRS, which is one of the Citizens Band Radio Services, includes fourteen channels in the UHF 460 MHz band. There are a number of commercially available two-way radios that are designed for use with the FRS. The increasing use of both portable two way radios and global positioning systems has led to proposals to incorporate GPS receivers into portable radio devices.
The first combined portable GPS receiver and two-way radio unit that is capable of displaying the location of at least one other such unit (as well as its own location) was recently developed by Garmin International, Inc. of Olathe, Kans. and is described in U.S. Pat. No. 6,373,430 (hereinafter the “'430 patent”). The combined global positioning system receiver and two-way radio unit of the '430 patent is capable of communicating with one or more other such units over a wireless radio network, wherein each of the units is adapted to transmit over the network radio signals indicative of that unit's location. The GPS/radio unit includes a GPS receiver for receiving satellite signals from a plurality of satellites, a processor coupled with the GPS receiver for calculating the location of the GPS/radio unit as a function of the received satellite signals, and a radio receiver coupled with the processor for receiving the radio signals transmitted by the other units. The processor is adapted to identify the location of the other units based upon the received radio signals. The GPS/radio unit also includes a display for indicating its own location as well as the location of at least one of the other units. The disclosure of the '430 patent is hereby incorporated herein by this reference as if set forth in its entirety.
The GPS/radio unit of the'430 patent includes a portable, handheld housing for housing the unit electronic components, e.g., the GPS receiver, the processor, the radio receiver and the display. However, the electronic components contained within the housing are vulnerable to potential harmful effects which may be caused by ingress of water (or other liquid) through the housing. Such ingress is of concern if the GPS/radio unit is dropped into a puddle, pond, river, stream or other body of water, if water or other liquid is splashed onto the GPS/radio unit, or if the user of the GPS/radio unit is caught in inclement weather such as rain or snow.
Thus, the inventors have recognized that it would be advantageous to provide a combined two-way radio communications unit and GPS navigation unit configured for wirelessly communicating with one or more other such units and which includes a substantially waterproof enclosure for protecting the electronic components housed therein from the potentially harmful effects of liquid ingress. It would be further advantageous to provide such substantially waterproof enclosure in a compact, robust yet relatively inexpensive form, the components of which are easy to fabricate and assemble.